Access mechanisms for magnetic tape cartridges, particularly those cartridges comprising relatively wide magnetic tape loaded on single spools used in helical scan read-write transports, include a housing (also referred to hereinafter as a "carousel") for transporting a plurality of such cartridges. Each cartridge is fetched from a location in the carousel by a fetching apparatus, loaded into a tape transport and read magnetically, then returned to the carousel.
Prior art carousels have been built in both circular and rectilinear configurations. In systems utilizing rectilinear array cartridge housings, the machanisms for locating the desired cartridge at the fetching apparatus require two degrees of freedom (X and Y) to retrieve the desired cartridge. However, such housings have the advantages of large capacity and compactness.
In other systems, cartridge housings are arranged in a circle for which the cartridge locating mechanism requires only one degree of freedom (rotation) for cartridge retrieval. While the mechanism for locating cartridges stored in a circular housing at the fetching apparatus is simple, the number of cartridges which can be conveniently stored in such housings is necessarily limited. Furthermore, as the number of cartridges to be housed increases, the radius, and hence the size, of the housing unit must increase disproportionately. See, for example, U.S. Pat. No. 3,953,890.